Curve adaptation effects on high-level facial-expression judgments are predicted to have the same form as low-level aftereffects

Abstract

Hong Xu et al. [Hong Xu et al, 2008 Journal of Neuroscience 28(13) 3374-3383] recently showed that adaptation to curved lines can affect high-level perception of emotional affect in faces, presumably by modifying the perception of mouth curvature. For the patterns tested so far, the effect increases as the adaptation pattern curvature increases. However, standard low-level aftereffects like tilt and motion aftereffects (TAE & MAE) typically show an S-shaped curve, with a decline in aftereffect strength for test patterns sufficiently different from the adaptation stimulus. In computational models of the TAE, the S-shape reflects adaptation in neurons that prefer a particular orientation, with neurons preferring very different orientations having little adaptation and thus showing weaker aftereffects. To see whether a similar explanation might apply to curvature/emotion aftereffects, we adapted an existing model of the TAE for use with curved lines and added processing for emotion judgments. We found that the model replicated the existing data on high-level effects of low-level adaptation, but strongly predicted an S-shape, ie that sufficiently large curvature values would lead to a lower effect. This prediction can be tested in humans, potentially helping to constrain the properties of the neurons underlying the effect